U.S. Pat. Nos. 4,164,755 and 4,165,560 of Matsumoto disclosure a pick-up stylus for use with a capacitive information disc. The stylus is fabricated from a tapered diamond support element having a plurality of conical portions with a common axis. Two of the conical portions are separated by an electrode bearing surface. A record engaging the surface is provided in a tip region substantially orthogonal to the electrode bearing surface. The diamond support element includes a pair of converging flat surfaces in the tip region which are deposed such that the intersection of the converging flat surfaces with the record engaging surface defines the side edges of the record engaging surface. The intersection of the converging flat surfaces with a conical portion remote from the electrode bearing surface forms a prow.
The stylus of Matsumoto may be manufactured by grinding a conical surface at one end of a diamond element. An electrode bearing surface is formed in the region of the conical tip and a record engaging surface is made substantially orthogonal to the electrode bearing surface.
Keizer in U.S. Pat. Nos. 4,104,832 and 4,162,510 has disclosed a capacitive information disc keel-tipped playback stylus. The terminating portion of the stylus is shaped to have a prow, a substantially flat rear surface remote from the prow, a pair of substantially parallel side surfaces extending from the side edges of the rear surface, a bottom surface extending from the bottom edge of the rear surface, and additional surfaces extending from the prow intersecting the bottom and side surfaces.
The keep tip stylus may be formed with an abrasive lapping disc having a deep, coarse-pitched groove. The tip is fabricated from a tapering support element having a tip which is defined by a prow and a substantially flat, "V"-shaped rear surface remote from the prow. The lands of the lapping disc lap the shoulders of the stylus and the walls of the abrasive groove form the substantially parallel side surfaces.
In order to reduce the cost of manufacturing a capacitive information disc playback stylus, it is advantageous to have a dielectric support element, such as diamond, sapphire and the like, mounted on a shank which may be, for example, a metal such as titanium. Such styli are common for use with audio records. Audio styli often have a conical-shaped tip. However, since the width of the information track in a capacitive information disc is substantially smaller than the information track recorded in an audio record, the terminal portion of the dielectric support element must be appropriately shaped.
One method of employing a shanked dielectric support element in a capacitive information disc playback stylus may be found in the copending application of Dholakia entitled "Playback Stylus and its Manufacture", Ser. No. 292,057, filed Aug. 12, 1981. A dielectric support element having a conical body terminating at a constricted tip is employed in which a flat surface on which a conductive layer may be prepared is lapped in the tip region followed by the formation of a disc engaging structure such as a keel tip.
I have found an alternate inexpensive means for converting a shanked dielectric support element to a relatively low cost capacitive information disc playback stylus.